从子 JPanel 返回一个值给父 JFrame

Question

I have a MainFrame class where I hold a JFrame and open a new JPanel as LoginPanel . In this LoginPanel class I have a login button and an ActionListener . The action listener should check the login credentials and then return to the MainFrame class any value maybe a boolean so I can open a new JPanel for the corresponding user:

public class MainFrame extends JFrame {
...
this.loginPanel = new LoginPanel();
this.add(loginPanel);

--> Here I would like to open a new JPanel and open a new JPanel 
    for the logged in user based on the value returned by the LoginPanel

...
}

public class LoginPanel extends JPanel{
...
// Create the action for the login button
   loginButton.addActionListener(e -> {
       // TODO: check if the given username is available
       // TODO: return maybe a boolean so we know that the user logged in succesfully
   });

I would be very thankful for any Idea on how to change my software design to implement this logic. Cheers!

Answer 1

Your question involves multiple steps, I'm afraid, but the bottom line is how to get one object to communicate with another, and the standard way to do this is by calling public methods of one into the other. One simple way is to give your LoginPanel class a MainFrame field, one that is filled via a constructor:

public class LoginPanel {
    private MainFrame mainFrame;
    private JButton loginButton = ....;
    
    public LoginPanel(MainFrame mainFrame) {
        this.mainFrame = mainFrame;
        
        loginButton.addActionListener(e -> {
            // extract the key properties from this class
            // such as text in a JTextField and the char[] in a password field
            // test it for appropriateness, and then send the information 
            // to the mainFrame object by calling a method
            
            // e.g.,
            // mainFrame.userVerified(/* boolean test in here */);
            
            // e.g.,
            mainFrame.userVerified(
                    userNameField.getText().equals(someUserNameVariable)
                    && Arrays.equals(passwordField.getPassword(), someCharArrayVariable));
        });
    }

So MainFrame would need to pass itself into LoginPanel:

public class MainFrame extends JFrame {
    public MainFrame() {
        // ...
        loginPanel = new LoginPanel(this);
        add(loginPanel);
        // ...
    }
    
    public void userVerified(boolean verified) {
        // act on it, swapping JPanels using a CardLayout
    }

A better solution, one that "scales well" is to separate concerns, the GUI from the non-GUI model and use a Model-View-Controller or similar type structure, but for your purposes, that may be over-kill at this point.